Power steering apparatus



0d. 29; 1946. w DAVIS POWER STEERING APPARATUS Filed Sept. 26, 1944Patented Oct. 29, 1946 UNETED STATES PATENT OFFlCE POWER STEERINGAPPARATUS Francis W. Davis, Belmont, Mass.

Application September 26, 1944, Serial No. 555,812

3 Claims. 1

This invention relates to power steering apparatus particularly suitablefor vehicles, and more particularly to heavy vehicles such as trucks,buses, construction vehicles, air craft, or the like.

One object of this invention is to provide a motor mechanism coaxialwith a hand controlled steering shaft, thus avoiding the use of powercylinders projecting outwardly from the shaft at inconvenient angles andyet to provide a; balanced hydraulic structure without unduecomplications. ihis provides greater compactness in the mechanism whilefacilitating its assembly and disassembly with respect to the vehicle.

A further object is to provide a construction in which the full area ofthe pressure actuated piston at both ends is utilized.

Another object of the invention is to avoid the necessity of amultiplicity of Stllfiiilg boxes.

Still another object is to provide the advantages of open valvecharacteristics of the structure shown in my Patent No. 2,213,271,granted September 3, 1940, in a structure where the pressure cylinderand piston is coaxial with the steering post.

Still another object is to provide a centering valve mechanism whichdoes not require hydraulic connections.

For a more complete understanding of this invention, reference may behad to the accompanying'dra-wing', in which Figure 1 is a centrallongitudinal sectional view through the lower portion of the steeringpost,

including the hydraulic motor and valve mechthreaded as at 3 and is inmating relation to an internally threaded opening i in a piston 5slidably mounted in a motor cylinder 6 arranged coaxial with the shaftl. At one side the motor cylinder 8 has an extension I through whichextends a rock shaft 8 having a gear segment 9 secured thereto, whichengages the teeth of a rack it set into a side face of the piston 5between its ends. As shown the piston 5 has a pair of spaced heads M andI5 which are provided with piston rings It for close engagement with thecylinder wall. For purpose of manufacture the piston is provided with acentral opening therethrough of which the threaded socket 4 forms apart, but the lower end of this opening is closed off as by a threadedplug 29 so that in use the entire lower face of the piston is accessibleto fluid under pressure introduced within the lower end of the eviinder.Preferably a by-pass channel 2;! is provided from the upper-end of thecylinder around the soc e portion and into the chamber 22, the lower endof which is closed off by the plug 26.

Attached to the upper end of the motor cylinder 6 is a valve cylinderwhich comprises a head 25 common to the motor cylinder 6 and to thevalve cylinder, a tube 21 which forms th main portion of the valvecylinder, and a domed head 28, the

head 28, the tube 21, and the head 25 being secured together as by tiebolts 39. Within the tube 27 is slidably mounted a valve 3! throughwhich and coaxial therewith the shaft I passes. The valve 3! may rotaterelative to the shaft l and "to-this end thrust ball bearings 32 and 33may be provided therebetween. The shaft l is permitted a slightlongitudinal motion, this longitudinal motion serving to move the valve3| axially relative to the tube 21, the inner wall of which provides aseat for the valve. This annular seat is provided with three annularports, a centra1 port 35 into which fluid under pressure may beintroduced, as through a pressure line 36, and a pair of dischargepassages 3! and 33 on opposite sides thereof. The valve is provided withtwo annular ports 4% and 4 I. In the central position of the shaft I,the ports ill and 4| slightly overlap both the pressure supply ports .35and the discharge ports 31 and 38 so that passage of fluid is permittedfrom the supply pipe 3% to both of the discharge pipes d2 and 43, thedischarge pipe 42 communicating with the discharge port 31 and thdischarge pipe 43 communicating with the discharge passage 38.

As shown best in Figure 3, the valve passage 41 leads through a passage50 to the lower end of the motor cylinder, while the valve passage 4!]leads through a passage 5| to the upper end of the motor cylinder 6, andalso leads through a passa e 52 to the interior of the valve chamber 53within the head 28. It will be noted that a slight displacement of thevalve 31 axially, say, to the right in Figure 3, will partly close offits communication with the pressure port 35 and increase itscommunication with the discharge port 38, this tending to lower thepressure within the valve passage 4| and consequently tending to lowerpressure beneath the motor piston, While at the same time the valvepassage 40 comes into 3 freer communication with thepressure passage 35andinto less free communication with the discharge passage 31, thusincreasing pressure above the piston 5. This tends to move the pistondownwardly or to the left in Figures 1 and 3, and thus to return thevalve 3| to its mid-position where the pressures on both sides of thepiston are e ual. Turning of the valve shaft I, however, acts to movethe shaft axially with reference to the piston 5 and thus throw thevalve out of its central position in such a direction as to tend tocenter the valve 3| again, so that the effect is to change the positionof the piston within the cylinder, and thus to change the angularposition of the shaft 8, which is connected through the usual link tothe steering draw bar A, as shown in Figure 4. The effect of turning theshaft I is thus to produce a steering effort to the vehicle, which isfurther enhanced by the power effect of the fluid pressure against thepiston 5. So long as the resistance to the turning of the rock shaft 8by the turning of the steering shaft I, which acts to displace thepiston 5 lengthwise of the shaft and thus to rock the gear segment 9, isinsufficient to displace the shaft axially and thus to move the valve 3|from its central position, steering is effected by hand. However,whenever this resistance exceeds this sufliciently,-the valve 3| isdisplaced from its central position, resulting in a fluid pressureunbalanced at opposite ends of the piston in a direction to move thepiston in the same direction that it is urged by the manual rotation ofthe steering shaft. This condition persists only so long as theshaft 8is in an angular position differing from that corresponding to theangular position of the steering shaft with the valve in its centralposition so that as soon as the power means has moved the steeredportion to such relation, the application of power to the steeringaction stops.

It is important that the valve 3| be urged toward its central positionwith reference to its seat entirely independent of pressure exertedthrough the fluid pressure mechanism, and to this end dished springwasher means is shown herein, one or more spring dished washers beingpositioned at 60 and bearing between the valve 3| and its casing member21 and the head 25. As shown these spring washers bear between a washer5| bearing against the inner upper raceway of the ball bearing 33 and ashoulder '52 of the cylinder head 25, and a washer 65 hearing againstone end of the tube 2'! and also against a washer 66 at the end of thevalve 3|. The dished spring washers thus act as a centering device forboth directions of motion of the valve 3| away from its centeredrelation, since they tend to separate the washers 62 and 65 theirmaximum distance.

It will be noted that the steering shaft passes through a bushing 10through the cylinder head 25, a light coil spring 1| bearing between ahead 12 of this bushing and a collar I3 bearing against the inner wallof the cylinder head. A similar spring 12!] is interposed between anannular shoulder 12| on the shaft and a packin 122 bearing against apartition I23 of the member 28 and through which the shaft passes. Theeifective pressure of the fluid within the motor cylinder above thepiston and tending to press the piston downwardly is thus decreased bythe effective area of the shaft through the outside diameter of thebushing 12 as at the line a-b. Pressure on the upper side of the pistonis, however, communicated into the chamber 53, and this'is'eilective topress the shaft downwardly by the effective area at the outside diameterof the valve 3| along the line c-d, diminished by an upward pressure onthe effective area of the shaft at e) where it passes through the upperend of the member 28. By so proportioning the parts that the effectivearea along the line cd is equal to the sums of the areas at a, b and e,f, the effective downward pressure area for the piston 5 is its entirearea, which is thus equal to the effective area beneath the piston. Thusthe pressure areas are balanced in both directions so that the effect ofthe steering shaft acting as a piston rod for the piston 5 isneutralized.

modifications might be made without-departing from the spirit or scopeof this invention.

I claim:

1. A steering mechanism comprising a manually rotatable steering shafthaving a threaded portion and mounted for limited axial motion, a fluidmotor .cylinder coaxial with said shaft, a piston slidable within saidcylinder and having a threaded opening into mating relation to whichsaid threaded portion extends, a steering part operatively connected tosaid piston to be moved by axial motion of said piston, a valvesurrounding and controlled by axial motion of said shaft and controllinthe supply of fluid within said cylinder on opposite ends of saidpiston, and means tending to center said shaft axially.

2. A steering mechanism comprising a manually rotatable steering shafthaving a threaded portion and mounted for limited axial motion, a fluidmotor cylinder coaxial with said shaft, a piston slidable within saidcylinder and having a threaded opening into mating relation to whichsaid threaded portion extends, a steering part operatively connected tosaid piston to be moved by axial motion of said piston, a valvesurrounding and controlled by axial motion of said shaft and controllingthe supply of fluid within said cylinder on opposite ends of saidpiston, and dished washer means tending to center said shaft axially.

3. A steering mechanism comprising amanually rotatable steering shafthaving a threaded portion and mounted for limited axial motion, a fluidmotor cylinder coaxial with said shaft, a piston slidable within saidcylinder and having a threaded opening in one end into mating relationto which said threaded portion extends, the opposite end of said pistonpresenting its complete area to fluid pressure between it and theadjacent end of said cylinder, a cylinder head at the opposite end ofsaid cylinder through which said shaft extends, a valve cylinder coaxialand rigid with said motor cylinder and through opposite ends of whichsaid shaft extends, a valve slidable within said valve cylinder andthrough which said shaft extends and mounted valve cylinder between saideffective areas of said shaft in said valve cylinder exposed to ressurein opposite directions to substantially balance the effects of fluidpressure acting in opposite directions on said shaft, a, steered part,and operative connections from said piston to said steered part.

FRANCIS W. DAVIS.

